Transformer core and winding



Aug. 17, 1965 A. A. HALACSY TRANSFORMER CORE AND WINDING Filed Aug. :5, 1960 IN VEN TOR ANDREW A. HALACSY BY M ATTORNEY United States Patent 3,201,734 TRANSFORMER CURE AND WINDING Andrew A. Halacsy, Elizabeth, N.J., assignor to Federal Pacific Electric (Iompany, a corporation of Delaware Filed Aug. 3, 196%, Ser. No. 47,20ll

7 tCiaims. (Cl. 336-22l) This invention relates generally to a transformer core and winding and, more particularly, to a transformer core of toroidal configuration and an improved winding arrangement therefor.

The core of wound-core power transformers is virtually universally of rectangular shape and is formed by suitably winding sheet steel to build up a laminated core. The rectangular core shape inherently involves whole long portions of the core to serve only to complete the magnetic circuit connecting the ends of the core portion that actually is encircled by winding. This entails excessive weight and cost of special alloy steel, and it entails correspondingly wasteful volumes of steel in which losses occur. Further, the proportions of rectangular core transformers are limited by existing coil winding apparatus.

The core of such transformers is often of rectangular cross section, or the cross section may be stepped to approximate a circle. The rectangular cross section has certain pronounced deficiences and disadvantages. The convolutions of the copper coil or winding about the core in the complete transformer have sharp bends at the corners of the rectangular cross section core, an arrangement which produces mechanical and thermal stress concentration points which weakens the coil. The sharp corner bends also increase the overall space requirement of the coil. In the case of current of short-circuited magnitude passing through the convolutions, the conductor lengths extending parallel to the major axis of the core tend to expand away from the core. This tends to distort the convolutions of wire and causes an increase of stress concentration at the corners of the coil tending to cut into the wire.

The aforenoted disadvantages of cores of rectangular cross-section are not present in a wound core of circular cross section. However, the latter is not desirable because it results in an increased mean length of the magnetic loop and increased core weight compared to a rectangular-section core of comparable coil cross-sectional area.

One important object of the present invention is to minimize the aforenoted deficiencies. More specifically an object of this invention is to provide an improved transformer having a minimum total weight of core and winding, having a minimum cost of material and minimized losses per kva. Pursuant to this object of the present invention, an improved transformer has been devised having toroidal core of generally elliptical cross section and having the current-carrying windings of like shape distributed about the core circumference.

Another important object of thevpresent invention is the provision of a core and winding arrangement which can Withstand heavier short circuit currents than a comparable core of rectangular cross section and which does not have concentrations of mechanical stress and of temperature-rise which characterize transformers having a core of rectangular cross section. The core of the present invention and its windings are lighter in weight and more economical than either. a comparable circular or rectangular cross section core and winding arrangement.

In a toroidal transformer, the distance along the inner circumference of the core is substantially less than that along the outer circumference, thus providing less space available for the conductors along the inside surface of Patented Aug. 17, 1965 the wound core than along the outer surface. A feature of the invention resides in a novel distribution of conductors in a toroidal transformer, to take this effect into account. The novel transformer detailed below involves a series of conductors that lie at a common level at the outer circumference but which extend in regular repeated sequence at different levels at the inner core circumference.

in a more specific aspect, each turn of the winding is composed of wires connected in parallel. These are wound in a manner such that the wires of the same turn are disposed in superposed relation, at successive levels, at the inner circumference of the core, and the same wires are disposed in side-by-side relation next to each other at a common level at the outer circumference of the core. in this manner the wide difierences between the inner diameter and the outer diameter of toroidal core are made compatible with an orderly conductive winding; and furthermore the adjacent wires require minimal insulation for their turn-voltage only and relatively heavy insulation is provided only between different layers.

Yet another object of the present invention is the provision of a novel toroidal power transformer of generally improved design and construction.

The illustrative embodiment of the invention, which has been outlined above as incorporating certain novel features forming part of the invention, is more fully described in the remainder of this specification, from which further novel features and objects and advantages will become apparent. In the following description reference is made to the accompanying drawings forming part of this disclosure, in which drawings:

FIG. 1 is a transverse sectional view showing the core and windings of a transformer formed in accordance with the present invention;

FIG. 2 is a sectional view taken on the line 22 of FIG. 1; and

FIG. 3 is an enlarged fragmentary view of area 3 of FIG. 2 and is illustrative of the manner of winding an inner winding layer in accordance with the present invention.

Referring to the drawings, and more particularly to FIGS. 1 and 2 thereof, there is shown a portion of an electrical transformer iii of toroidal configuration, said transformer comprising a toroidal core 12 of a suitable magnetic material, such as silicon steel. Surrounding the core are spaced layers 14, 16, 18 and 20 of insulation, the

inner winding which is composed of two spaced layers 22 I and'2 2a, and the outer single winding layer 24. The innet winding layers 22 and 22:: are disposed between the insulation layers 14 and 16, and 16 and 18, respectively whereas the outer winding layer 24 surrounds insulation layer 18. Either winding may be the high voltage winding with the other being the low voltage winding, the high voltage winding being the primary and the inner Winding of the illustrated embodiment. The space between the core and layer 14 of insulation is filled with a suitable filler material 26, such as sand. The temperature differential between the core and the outer surface of the transformer is substantially reduced by the provision of cooling fins 2% as described in detail in my copending application Serial No. 47,201, filed August 3, 1960, said application being assigned to the assignee herein. The Cooling fins include a peripherally continuous arcuate part 30 which is disposed in the heat path between the inner and outer windings. More particularly, part 30 is disposed between layers 18 and 18' of insulation, a series of convolutions of the Winding layer 24- extending around said part.

Pursuant to the present invention, the core is of generally elliptical cross section having the ratio of the major and. minor axes thereof within a predetermined range as will be described indetailbelOW. The core is formed of strip steel stock wound to form stacked layers or laminations and to assume an overall toroidal configuration. The groups of layers are of overall reduced width at increments spaced. from the center of the coreto generate the 'desi'redstepped cruciform or elliptical cross section. More'pa'rticularly; the group a of layers at the center of thecoreiis of. maximum width and defines approximately. the majdr axis 32. of the core, the groups b, c, d, and e bei g progressively narrower in stepped. increments and symmetrically disposed with respect to the axes of the core the group e being ofminimurn Width and defining approximately the minor axis 34 of the core. Thus the gi'oi ps of layers generate an overall elliptical cross section whichlisv assumed .bythe layers of insulation and windings. The selectedratio of the major and minor axes is such as toiprovidea minimun1 totalweight of core andrwindingsjorfniinimum total cost thereof, or in the range theresen es. The minimum weight occurs where the ratio of the, major and minor axes of the core is approximately in accordancewith the following formula:

lbs/cu. in. steel AST v lbs/cu. in. wire A N +A N Thev minimum cost occurs when the same ratio is approximately in accordance with the following formula:

AST, l bs. WlI6) A N +($/lbS.. wire) A N The notations used in the above formulae are. as follows:

M :major elliptical axis m=minor elliptical axis AST==cross sectional area ,of the steel in the core A =cross sectional area of one primary turn A =cross sectional area of onesecondary turn Nfznumb'er of primary turns Nz=n bt t of s qndary tu ns The values of core cross-section, the cross sectional areas of the conductors, and the numbers of turns in the windings are all values that are determined by. usual transformer design procedures.

e twq resltlting ratios will. not be the same and a practical compromise between the two ratios is perfectly made. In a certain application, given here by way of example only, these values resulted in a range between 2 and 3.6 and the value of 2.16 was selected for manufacturing reasons and because a lower ratio is more favorable from the standpoint of short circuit conditions; An elliptical cross section core and its windings within the aforenoted range, is lighter in weight and more economical than a eithera comparable circular or rectangular cross section core ,and winding arrangement. Theaforenoted elliptical core and winding arrangement can withstand heavier short circuit currents than a comparable core of rectanguenemas ,pair of turns of wire 38.

ingarrangement may be used for any desired winding layer or layers in a toroidal transformer. 'One turn of conductoris composed of a plural number of wires connectedfin parallel. The number of parallel-connected wires used should be related to the ratio of the outer diameter of the toroid to the inner diameter of the toroid. Where this ratio is expressed in decimal form, it is desirable that the number of wires should be an integer that is less than 1.25 times this ratio but greater than one integer lower than the integer in the decimal ratio of toroidal diameters. A practical ratio of such diameters is three, enabling three parallel wires to be used in the single phase toroidal transformer of the illustrated embodiment. The three wires 36, 38 and 4d of a turn are wound in a manner that such Wires are disposed in superposed relation at the inner circumference of the core and are disposed in immediately adjacent side-by-side relation at. the outer circumference of the core. The three wires 36, 38 and 40 are connected in parallel at the ends of the winding. Said wires are disposed. uniformly in sequence at the outer circumference .ofthecore and collectively define the layer 22'Whose' thickness corresponds to a single wire diameter. At the inner circumference of the core the Wires 36, 38 and 40 are superposedon each other to form an inclined threetier layer. Wire 36 forms the outer tier, wire 38w rests on the. outer tier 36, in staggered relation, sothat each turn of wire 38 .is supported by a pair of turns of wire 36. Similarly, the wire deforms the innermost tier and the turns thereof are staggered-with respect to wire 38 so. that each turn ofwire 40 is supported on an adjacent wires of the layer require insulation for their turn-voltage only and a common layer insulation 16 is provided over are inclined to the radius of the core drawn to any such" turn. This arrangement facilitates the winding of the Wires on. the core. Thethree wires may be wound successively or simultaneously. Where the wires are wound simultaneously, the wires at the inner circumference will be suitably guided .in inclined relation at the initiation of the Winding operation and thereafter the subsequent windings .will fall into position on the previously woundnext adjacent turns. Where the wires arewound individually, thefirstwire Suds wound: as a simple toroidal winding leaving gaps at the outer circumference'to accommodate the wires 38 and 40. The second wireis wound over wire 36 dropping into position on pairs of adjacent turns of wire 36 at theinner circumference and intotthetgaps. at the outer circumference immediately adjacentto the turns of 'wirefaao Similarly the third wire til-is Wound over wire 38at the inner circumference,

dropping-into positionin the space remaining at the outer circumference.

Various additional modifications of the above embodiment'of .the invention will readily occur to those skilled the .art, andtherefore the invention'should be broadly construed in-accordance with its full spirit and scope,

Having thus described my invention, what I claim as new and desire tosecure by Letters Patentis:

1.. An electrical transformer having a toroidal winding of steel strip forming a magnetic core, the wide face] of the strip being parallel'to the toroidal axis, and a winding of.wire extendingaround said core, said coreand I winding generating an essentially elliptical cross section,

the. major axis of the ellipsebeing parallel to the axis of the toroidal core, and the ratio of themajor axis of the ellipseto its minor axis being between 2 and 3.6.

2.-A toroidal core for an electrical transformer, said core.being formed of strip stock of various widths wound about an axisto form stacked laminations Whose layers are disposed. at successively different distances fromsaid axis, and said core being of essentially elliptical cross section whosemajoraxis is parallel to the axis of the toroidal core.,

3. A toroidal/electrical transformer, including a toroidal core formed of strip magnetic stock whose width differs in steps and is woundtoform stacked groups of laminations each having itswide faceparallel to the to- In this manner the adjacent of the major to minor axes roidal axis, said groups being arranged to form an essentially elliptical cross-section whose major axis is parallel to the toroidal axis, spaced layers of insulation and windings extending around said core, and inert filler material filling the spaces between the stepped groups of strip stock and the innermost layer of insulation.

4. In an electrical transformer, a toroidal steel core having primary and secondary windings extending therearound, said core and windings generating an approximately elliptical cross section having the ratio of the major and minor axes between the two values resulting from the following formulae: 1

lbs/cu. in. steel AST lbs/cu. in. wire A N +A N u. in. steel $/lbs. steel lbs/cu. in. Wire AST wire wire the aforenoted notations used being as follows:

=major elliptical axis m=minor elliptical axis AST=cross sectional area of the steel in the core A =cross sectional area of one secondary turn A =cross section-a1 area of one secondary turn N =number of primary turns N =number of secondary turns 5. A toroidal core for an electrical transformer of approximately elliptical cross section, said core being formed of strip steel stock of widths diifering in steps, wound to form stacked groups of symmetrically disposed laminations in planes parallel to the toroidal axis, said groups being arranged to approximate an elliptical cross-section whose major axis is parallel to the toroidal axis, said core having primary and secondary windings thereon, the ratio of the elliptical cross-section at the mean depth of the windings being between the values resulting from the following formulae:

lbs/cu. in. steel AST AST AIN1+ $llbs. 1

wire

the aforenoted notations used being as follows:

6, In an electrical transformer, a toroidal core having a winding extending therearound, said winding having the turns thereof composed of a plural number of wires connected in parallel, the wires of the same turn being disposed in superposed relation at the inner circumference of said core and in adjacent side-by-side relation at the outer circumference of said core, said wires being insulated from each other for their turn-voltage only and having layer insulation thereover.

7. In an electrical transformer, a toroidal core having a winding extending therearound, said winding having the turns thereof composed of a plural number of wires connected in parallel, the wires of the same turn being disposed in superposed relation at the inner circumference of said core and in adjacent side-by-side relation at the outer circumference of said cor References Cited by the Examiner UNITED STATES PATENTS 513,420 1/94 Rowland 33661 546,476 9/95 Scott 336 853,843 5/07 Troy 336-61 1,102,513 7/14 Johannesen 336229 X 1,320,980 11/19 Bowman 336-229 X 1,362,138 12/20 Pratt 336229 X 1,421,899 7/22 Bingay 336--225 X 1,503,977 8/24 Burnham 336*186 1,531,681 3/25 Auty 336229 X 1,623,345 4/27 Hopkin 33661 2,348,325 5/44 Brown 336-186 2,401,984 6/46 Steinmeyer 336-225 X 2,780,787 2/57 Somerville 336234 2,783,441 2/57 Camilli et a1 336180 2,863,130 12/58 Gray et al. 336180 X 2,896,182 7/59 Pruneau 336-234 2,899,631 8/59 Cushman 336-96 X FOREIGN PATENTS 670,014 4/52 Great Britain.

LARAMIE E. ASKIN, Primary Examiner.

MILTON O. HIRSFIELD, JOHN F. BURNS,

Examiners. 

1. AN ELECTRICAL TRANSFORMER HAVING A TOROIDAL WINDING OF STEEL STRIP FORMING A MAGNETIC CORE, THE WIDE FACE OF THE STRIP BEING PARALLEL TO THE TOROIDAL AXIS, AND A WINDING OF WIRE EXTENDING AROUND SAID CORE, SAID CORE AND WINDING GENERATING AN ESSENTIALLY ELLIPTICAL CROSS SECTION, THE MAJOR AXIS OF THE ELLIPSE BEING PARALLEL TO THE AXIS OF THE TOROIDAL CORE, AND THE RATIO OF THE MAJOR AXIS OF THE ELLIPSE TO ITS MINOR AXIS BEING BETWEEN 2 AND 3.6. 